So this is only about the light theme. The dark theme isn't quite so "dark," but does feel better to use.
Obligatory these are just my subjective opinions about the style, so de gustibus non est disputandum and all that jazz.
I tried version 3.3. The first thing that caught my eye was the huge wasted space on each side of the forum, as if it was meant for smaller screens (like iPads)? This goes away when I expand to only half my screen or I increase the font size, which I probably would do anyway, so it's not a big deal.
The "corporate" effect comes out chiefly in the color, or lack thereof. It's a lot of gray: light gray background that gives off a hospital or cubicle space. The rotating polygons would have to go - it's generic filler that evokes that barebones, "sleek" minimalism so many offices are fond of. And the accent colors are all very safe. They don't really change the style at all. The default I would even call "facebook blue" (or Fedora blue): safe sky blue that just recedes into the background. It's not complementary with dark themes either.
I think these reasons make it feel more "corporatized," though something like hospital fits as well. It's not brash or exciting. There's no edge. Great for a forum about an established company, less great for a small niche community centered around classic video games.
As I mentioned, I don't hate it, and by pointing this out it can't be helped that these features feel exaggerated. I wouldn't be bothered if this was the theme, but I do get that corporate, sterile, old-hat feel to it.
